I was in a 12 week course at the Bell System Center for Technical Excellence in Lisle, IL in 1980. We were treated to previews of unreleased technology. One of the stranger items was a D to A audio transducer. The phone was on a digital line and the earpiece had a set of semi-circular elements whose size represented the weight of a bit in the digital data. It was a simple electro-mechanical device. Fidelity was acceptable. Not as spiffy as the integrated circuits with u-law or a-law DtoA converters used now. The switch room had an old #1 ESS with core memory and ferrite sheet memory. All discrete components. Equipment frames were 6 feet tall and 30 ft long. Loading the call store was a 3 week operation. The "code" arrived on aluminum plates with ferro-magnetic squares representing bits of the 43 bit call processor. A milk carton size box held about 30 plates. It held a rack that could hang on the "card reader" to read the data into the core call store. Really primitive. The 30 MB hard disk had two surfaces with fixed head disks. It was spun with a washing machine motor with belts.
At the time I took the course, my duties at work included removal of analog O/ON carrier systems and installation of T1/T1C repeater bays and D4 channel banks.
I had a similar idea, but with series power-of-two weighted coils replacing the normal single speaker coil on a speaker cone driver.
I knew instinctively it wasn’t practical, and never tried to patent it. Also I didn’t have anywhere near the resources necessary to do so, at the time.
Undoubtedly many others had the same idea, at the time.